Downhole communication applications

ABSTRACT

In some embodiments, an apparatus and a system, as well as a method and an article, may operate to transform acquired data into transformed data using at least one transform selected from a plurality of transforms according to an optimization metric calculation that operates on single, fixed-length packets of the transformed data, and a preselected quality criterion threshold. Further activity may include transmitting an amplified version of an electrical signal in a geological formation, the electrical signal including the transformed data. The amplified version may be received, and further activity may include transforming the transformed data into an estimate of acquired data, the transforming using at least one transform selected from a plurality of transforms according to an optimization metric calculation that operates on single, fixed-length packets of the transformed data and/or the estimate, and a preselected quality criterion threshold. Additional apparatus, systems, and methods are disclosed.

BACKGROUND

Drilling rig operators often employ the use ofMeasurement-While-Drilling (MWD) and Logging-While-Drilling (LWD) toolsand services during drilling operations, to measure and/or log variousconditions within the borehole and/or the rock formations surroundingthe borehole. MWD/LWD tools utilize a variety of sensors to sample andaggregate digital values for real-time transmission to the surfaceduring drilling operations. The transmission scheme and channel mediummay vary. For example, they may include Mud Pulse Telemetry (MPT)through water and drilling mud, Electro-Magnetic-Telemetry (EMT) throughrock formations, and Acoustic Telemetry (AT) via the drill-string. Eachscheme typically employs some form of modulation (e.g.Pulse-Position-Modulation (PPM), Orthogonal Frequency DivisionMultiplexed (OFDM), and Direct Sequence Spread Spectrum (DSSS)) toincrease the reliability of communication through the associated medium.

When either OFDM or DSSS modulation are used, the transmitpeak-to-average-power-ratio (PAPR) is often poor (i.e., relativelyhigh), as compared to other processes, even though error rates may beimproved. As a result, a more expensive transmitter power amplifier,with a higher dynamic range, is often used to maintain a desired levelof reliability within a given communication system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates examples of scrambler transforms at the transmitterand the receiver, according to various embodiments of the invention.

FIG. 2 illustrates a bit-stream format concatenating packets of fixednumbers of bits, according to various embodiments of the invention.

FIG. 3 illustrates a bit-stream format concatenating fixed lengthpackets with SEED values, according to various embodiments of theinvention.

FIG. 4 illustrates a bit-stream format concatenating fixed lengthpackets with SEED and POLY values, according to various embodiments ofthe invention.

FIG. 5 illustrates transmission bit-streams that may be used to reducePAPR, according to various embodiments of the invention.

FIGS. 6-16 illustrate block diagrams of transmitters and receivers,according to various embodiments of the invention.

FIG. 17 is a block diagram of apparatus according to various embodimentsof the invention.

FIG. 18 illustrates a wireline system embodiment of the invention.

FIG. 19 illustrates a drilling rig system embodiment of the invention.

FIG. 20 is a flow chart illustrating several methods according tovarious embodiments of the invention.

FIG. 21 is a block diagram of an article according to variousembodiments of the invention.

FIGS. 22-24 illustrate additional block diagrams of transmitters andreceivers, according to various embodiments of the invention.

DETAILED DESCRIPTION

In some embodiments, data to be communicated within a drilling system,from sub-surface to surface, and vice-versa, is transformed by selectinga transform from a plurality of transforms to improve (i.e., reduce) thetransmit PAPR of the signal that carries the data within a rockformation using multi-carrier/waveform modulation, without materiallyreducing the decoding rate. The terms “rock formation” and “geologicalformation” are used interchangeably herein, referring in all cases tomaterials that make up the surface and subsurface of the Earth. Thesolution provided by this process can be used to more efficiently andaccurately communicate data within underground formations.

As used in this document, a “scrambler” is a processing devicecomprising electrical hardware that operates to manipulate a data streambefore transmission into a communications channel. The manipulations arereversed by a “descrambler” at the receiving end of the communicationschannel. Scrambler types may include additive and multiplicativescramblers. Scrambling is widely used in satellite, radio relaycommunications, and PSTN (public switched telephone network) modems. Insome embodiments, a scrambler is placed just before a FEC (forward errorcorrection) coder, or it can be placed after the FEC, just before themodulation or line code. A scrambler in this context has nothing to dowith encrypting, as the intent is not to render the messageunintelligible, but to impart useful properties to the transmittedsignal. For example, the scrambler may operate to transform digitalsequences into other sequences, without removing undesirable sequences,to reduce the probability of vexatious sequence occurrence.

Scramblers have been used in the past to “whiten” digitized data,providing adaptive equalization in a receiver, or flattening the powerspectral density of a transmitter's output. These uses are contrary tothe teachings provided herein, since the various embodiments operate tolocally flatten the time-domain transmission amplitude within a packet,and not the ergodic frequency content of the overall signal. Indeed, theuse of scramblers in various embodiments, as described herein, mayresult in greater frequency variance across subcarriers or spreadingcodes (e.g., in the case of quadrature amplitude modulation), andincrease the local periodic characteristic within modulated packets ofdigitized data, depending on the choice of modulation for eachsubcarrier.

To reduce PAPR in a transmitted signal, some embodiments include anapparatus electrically connected with a drill string configured toproduce electrical current in a rock formation comprising. The apparatusmay comprise a power source, and an amplifier electrically connected tothe power source. The amplifier is used to vary an adjustable voltageoutput to produce changes in electrical current traveling through a rockformation. The apparatus uses a controller that operates the amplifierto create a plurality of changes in the electrical current passingthrough the rock formation via multiple waveform modulation, wherein thecontroller formats digital data into packets using a transform selectedfrom a plurality of available transforms.

Transmitter embodiments may use a form of multiple waveform modulation,e.g. OFDM (orthogonal frequency-division multiplexing) or DSSS(direct-sequence spread spectrum). The multiple waveforms within OFDMmodulation aggregate a plurality of sinusoidal subcarriers orthogonalwith respect to each other, where each subcarrier is further modulatedusing more conventional modulation approaches, e.g. PSK (phase-shiftkeying) and QAM. The aggregation may cause constructive superposition,so that subcarrier amplitudes present large absolute amplitude peaksrelative to the average absolute amplitude over the symbol period.Hence, OFDM transmission signals often experience a poor PAPR, leadingto poor telemetry throughput unless circuit complexity is significantlyincreased.

Under a DSSS scheme, an aggregation of a plurality of chip sequences,preferably with low cross-correlation properties, is transmitted. Thus,DSSS transmission also may suffer from a poor PAPR.

Under either OFDM or DSSS, when the PAPR is poor, a more expensivetransmitter power amplifier, with a higher dynamic range, is often usedto maintain a desired reliability of communication. Various embodimentsdescribed herein operate to transform a packet of predetermined lengthinto OFDM or DSSS symbols with a reduced PAPR, reducing constraints onpower amplifier dynamic range, while providing the same communicationreliability.

Thus, some embodiments may include a system to communicate through arock formation that comprises a transmitter configured to modulate acurrent with transformed digital data and to transmit the modulatedcurrent through a rock formation. The modulated current may comprise asuperposition of a plurality of waveforms. The system may furtherinclude a receiver configured to demodulate the current, to select atransform from a plurality of transforms, and to use the selectedtransform to operate on the demodulated information, providing thedigital data forming part of at least one packet, using an errordetection code.

FIG. 1 illustrates examples of scrambler transforms 100, 102, 104, 106at the transmitter and the receiver, according to various embodiments ofthe invention. Thus at the transmitter, one embodiment uses a transformselected from a set of transforms 100, 104 where each comprises a linearfeedback shift register (LFSR) configured according to a polynomialdescriptor. Each register can accept an initial state value/indicatorfor the memory elements within the LFSR. The number of memory elementsmay indicate the largest possible cardinality of the transform set.Thus, the transmitter may have at least one scrambler 108 that includesone or more transforms 100, 104, perhaps taking the form of LSFRs, totransform, e.g. scramble, digital values according to a polynomialindicator and an initial value, possibly using Galois Field arithmetic(GF), such as modulo-2 arithmetic. The transforms 100, 102, 104, 106 mayalso be implemented with hardware or hardware executingsoftware/firmware instructions that provides a unitary transform,spherical codes, and other matrix transforms.

Some embodiments operate to communicate through a rock formation as asystem. The system may comprise a transmitter configured to modulate acurrent through the rock formation, where the current comprises asuperposition of a plurality of waveforms. The system may comprise aplurality of initial state indicators accessible to the transmitter toenable scrambling digital data. The system may further comprise areceiver configured to demodulate the signal provided by the current,and to select an initial state indicator from a plurality of initialstate indicators accessible to the receiver. The receiver may furthercomprise transforms 102, 106, perhaps taking the form of LSFRs, todescramble the transformed digital data using a descrambler 110 and anerror detection code to determine the digital data within at least onepacket. An initial value of all zeroes may operate to disable thescrambler 108 or descrambler 110.

FIG. 2 illustrates a bit-stream format 200 concatenating packets 201,202, 203 of fixed numbers of bits, according to various embodiments ofthe invention. Each packet 201, 202, 203 includes information in theform of data 204 (e.g., bits, bytes or words 206, 207, 208) and cyclicredundancy check information 205. In some embodiments, the bit-streamformat 200 is transmitted and received using scrambled data 204.

FIG. 3 illustrates a bit-stream format 300 concatenating fixed lengthpackets 301, 302, 303 with SEED values 309, according to variousembodiments of the invention. Here each packet 301, 302, 303 includesinformation in the form of data 304 (e.g., bits, bytes or words 306,307, 308), cyclic redundancy check information 305, and a SEED value309, which represents the initial content of an LFSR.

FIG. 4 illustrates a bit-stream format 400 concatenating fixed lengthpackets 401, 402, 403 with SEED and POLY values 409, 410, according tovarious embodiments of the invention. Here each packet 401, 402, 403includes information in the form of data 404 (e.g., bits, bytes or words406, 407, 408), cyclic redundancy check information 405, a SEED value409, and a POLY value 410, which represents the polynomial descriptorfor the transform that has been selected, perhaps to be implemented byan LFSR.

Thus, transmitters may operate to select different initial contentvalues, or SEEDs, for one or more LSFRs. Transmitters that operate inthis manner may transform a given set of digital data input bitsdifferently, using different SEEDs, resulting in potentially differentPAPR characteristics for each selection. The transmitter can theninclude the selected SEED within the bit-stream modulated fortransmission, as shown in FIGS. 3 and 4.

A controller within the transmitter may operate to account for the SEEDinitial value indicator when calculating the various PAPRs for eachtransformed digitized value, perhaps as part of calculating optimizationmetrics for each possible SEED given a LSFR configured to implement aparticular polynomial descriptor, POLY. Thus, transmitters in someembodiments may use the PAPR as a predetermined optimization criterion.In other embodiments, the SEED and/or POLY values that pertain to thetransform used at the transmitter may or may not (e.g., see FIG. 2) beincluded in the formatted bit-stream and/or encoded, modulatedwaveforms. Likewise, various receiver embodiments at the receiver may ormay not use any SEED and/or POLY values to decode transmitted packets.This tradeoff may involve additional receiver complexity (morecalculations), as various possible combinations for SEED and/or POLYvarious are tested to determine which produces a series of correctlyunscrambled packets.

In some embodiments, a controller calculates at least one optimizationmetric relating to a predetermined criterion (e.g., selecting athreshold acceptable error rate) for at least one transform within aplurality of transforms. The controller may include a memory device tostore one or more optimization metrics, as determined by a predeterminedcriterion. Memory devices may include one or more of a register or cachememory within a microcontroller or microprocessor, a register comprisingof digital logic within a programmable device and/or ASIC(application-specific integrated circuit), random access memory (RAM),and non-volatile storage, such as FLASH memory, programmable read-onlymemory, and/or a hard-drive.

The controller may operate to select a transform from a plurality oftransforms corresponding to a minimal (i.e. a metric near a minimum)optimization metric, such as the PAPR, or the minimum PAPR Likewise, thecontroller may operate to select an equivalent maximal (i.e. a metricnear a maximum) optimization metric, such as 1/PAPR, or the maximum1/PAPR.

FIG. 5 illustrates transmission bit-streams 510 that may be used toreduce PAPR, according to various embodiments of the invention. Here itcan be seen that scrambling the data with a fixed POLY value andoptimized SEED value results in a reduction of PAPR 514 given the sameinput data bitstream as in 512 that has not been optimized for PAPR.Even further reduction in PAPR may be achieved by determining anoptimized POLY value for a configurable LSFR scrambler in conjunctionwith an optimized SEED value for the configurable LSFR scrambler as in516 given the same input data bitstream as in 512 and 514. Forillustration purposes, FIG. 5 includes SEED and POLY values within thetransmission of the bit stream, slight increasing the time oftransmission. In practice, including SEED and POLY values within thetransmission may be useful to reduce receiver complexity. However, insome embodiments, the system may benefit from selecting and using anoptimized transform, saving time by not including the SEED and POLYvalues in the bit stream to be modulated.

Alternative embodiments of the optimization metric may us the estimatedprobability of receiving a packet in error, given channel stateinformation. Likewise, the optimization metric might comprise using theestimated probability of receiving the packet correctly (e.g., a packetrejection region may or may not be present in the metric).

A method embodiment operates to communicate through a rock formation bycalculating at least one optimization metric relating to a predeterminedoptimization criterion, using the optimization metric to select one of aplurality of initial state indicators available to a transmitter, andscrambling digital data using the selected initial state indicator(which may enable the receiver to perform an error-detection check).Additional activities may include transmitting the scrambled digitaldata through the rock formation using a modulated waveform comprising asuperposition of multiple waveforms, receiving the transmitted waveformfrom the rock formation, demodulating the received waveform into aplurality of demodulated values, and identifying packet errors using thedemodulated values, the selected transform, and an error detection code.

FIG. 6 illustrates a block diagram of a transmitter 610 and receiver612, according to various embodiments of the invention. FIG. 7illustrates a block diagram of a transmitter 710 and receiver 712,according to various embodiments of the invention. FIG. 8 illustrates ablock diagram of a transmitter 810 and receiver 812, according tovarious embodiments of the invention.

Referring now to FIGS. 6-8, it can be seen that a transmitter canoperate on a concatenated sequence of information (comprising SEED andPOLY values, as well as a data payload 622) 620. A transmitted CRCprocessor 624 can operate on its input (the information 620 in thiscase) to calculate and append a CRC value to the information 620. A FEC(forward error correction) encoder 630 may operate on its input (theinformation 620, augmented by an associated CRC value in this case,which provides augmented information 626) to calculate and append errorcorrecting code(s) to the augmented information 626, providingadditional information 628.

The output of the FEC encoder 630 (i.e., additional information isscrambled by a scrambler 632, which may comprise one or more transforms(e.g., transforms 100, 104), perhaps taking the form of LFSRs. Theoperation of the scrambler 632 may be influenced by POLY and SEED valuesselected by the transmission selector 634, which may in turn be selectedas fixed or variable values, perhaps according to minimal/minimum PAPRcalculations, maximal/maximum 1/PAPR calculations, or other metricoptimization calculations. The selected SEED and POLY values may beprovided to the concatenated sequence 620, as well as to the scrambler632.

The output of the scrambler 632 is modulated by the modulator 636 (e.g.,an OFDM or DSSS modulator), before entering the communications channel714 as transformed data 638. The transformed data 638 may be amplifiedusing a power amplifier (not shown at the output of the transmitter610).

A receiver 612 can operate to receive the transformed data 638, which isdemodulated by the demodulator 656 to provide demodulated data. Adescrambler 652 (which may be similar to or identical to the scrambler632) can operate on the demodulated data to provide descrambled data. AFEC decoder 650 can apply the error correcting code(s) to thedescrambled data to provide a decoded data sequence 640.

The demodulator 656 may provide either hard or soft detection. If softdetection is used, the payload bits may be estimated by the estimator642 and selectively applied, using the selector 644, so that the correctCRC appears, as calculated by the received CRC processor 646.

In FIGS. 7 and 8, the components of the transmitter 610 and receiver 612shown in FIG. 6 have been arranged in a different order, to permitprocessing acquired data (e.g., input bits 622) differently, providingessentially different transmitter/receiver combinations 710, 712 and810, 812. Thus, many embodiments may be realized.

For example, some transmitter embodiments use scramblers 632 that employconfigurable LSFRs transmit the polynomial descriptor, POLY, with theSEED descriptor, and may include one or both values within theoptimization metric and optimization criterion. The plurality ofavailable transforms may be implemented using at least one configurableLFSR used to receive a polynomial indicator from a plurality of possiblepolynomial indicators that described feedback connections to the LFSR.

In some embodiments, the optimization metric and predeterminedoptimization criterion in the transmitter may or may not use peak oraverage powers or amplitude or their ratios. Indeed, the POLY and SEEDindicators may or may not be transmitted along with the transformed data(e.g., see examples of different potential transmission bit streams 510,prior to transformation, shown in FIG. 5).

The plurality of available transforms within a scrambler may or may notutilize initial values identifying different transforms. Receivers mayor may not use formatted data to exhaustively search for sequences thatresult in determining the SEED and/or POLY values utilized by thetransmitter. The tradeoff in these cases may be receiver complexityversus bandwidth efficiency.

In some embodiments, a transmitter within a communications systemtransforms and transmits digital data within a packet using a modulationresembling the superposition of multiple waveforms. The transmittercomprises an amplifier having a peak output voltage with a selecteddynamic range, a plurality of available transforms, a transform selectorto select at least one of the transforms such that the modulated outputvoltage of the amplifier provides at least one packet of transformeddigital values that avoids non-linear distortion after the applicationof an interpolation filter, wherein the selected transform enables errordetection at the receiver. The interpolation filter allows the insertionof data into the bit stream, ahead of the amplifier. The transmitter maycomprise one or more connectors to provide connections to a drill stringand/or well casing.

In some embodiments, the transmitter includes a plurality of initialstate indicators, and an initial state indicator selector to select atleast one initial state indicator from the plurality of initial stateindicators to avoid non-linear distortion after the application of theinterpolation filter. In some embodiments, the transmitter includes ascrambler with a plurality of configurations, a plurality of initialstate indicators, a scrambler configuration indicator selector to selectat least one configuration from said plurality of configurations.

An apparatus may comprise a receiver electrically coupled to a drillstring to receive formatted digital data transmitted via multiplewaveform modulated electrical current through a rock formation. Thereceiver may comprise a sensor to receive a superposition of waveformsfrom the current in the rock formation, a demodulator to estimatetransmitted digital values from the superposition of waveforms receivedby the sensor, and a plurality of transforms to enable transforming thereceived, estimated digital values. The receiver may further comprise acontroller to select at least one transform from said plurality oftransforms and to transform the received, estimated digital values intodigital data representing data that was acquired by the transmitter.

The receiver may operate to demodulate multiple waveform modulationcomprising OFDM or DSSS. The transforms may comprise LSFRs, with theability to accept at least one initial shift register value from aplurality of possible initial shift register values. One or moreconfigurable LSFRs may be operable to receive a polynomial indicatorfrom a plurality of possible polynomial indicators describing feedbackconnections.

In some embodiments, a controller operates to select at least oneinitial shift register value from a plurality of possible initial shiftregister values, to implement the selection of a transform. Thecontroller may also operate to select at least one polynomial indicatorfrom a plurality of possible polynomial indicators to implementselection of a transform. The initial shift register and polynomialindicator value(s) may be selected at least in part based on saidestimated transmitted digital values. Other controller embodiments mayemploy a plurality of LFSRs configured using a corresponding pluralityof polynomial descriptors, corresponding to a plurality of polynomialindicators.

In some receivers, a scrambler may be configured to receive at least oneinitial state indicator from a plurality of possible initial stateindicators, to generate a sequence of numbers and transform saidestimated digital values. The associated controller may be configured toselect at least one initial state indicator from a plurality of possibleinitial state indicators used in the transformation of said estimateddigital values. The scrambler may be used to generate a sequence ofnumbers and transform digital data using Galois Field arithmetic.

The controller in a transmitter or a receiver may comprise a digitallogic circuit, or a microprocessor circuit, or a microcontroller circuitexecuting a program. A CRC processing module may be used to provide aCRC value within packets of formatted digital data, as part of thebit-stream. The CRC processing module can operate to check receivedestimated digital values, and to enable selection of at transformedreceived estimated digital values from a plurality of transforms.

The CRC processing module may be realized using either hardware and/orsoftware. The CRC processing module uses a sufficient number of bitsalong with a polynomial descriptor that, when combined, providesdecoding error detection to some desired threshold level of accuracy.

In some embodiments, a system may comprise one or more repeaters, eachincluding a transmitter and a receiver. The repeater may relay blindlyand/or decode and re-encode digitized data, wherein the re-encoding mayor may not use the same modulation coding scheme as the decoding. In thecase of re-encoding, the repeater may select its own transformindicator(s) via its own criteria or simply reuse the same SEED and POLYvalues obtained from the received signal.

In some embodiments, rock formation communication is initiated byselecting a transform from a plurality of transform available at thetransmitter, transforming digital data using the selected transform (soas to enable the receiver to perform an error-detection check), andtransmitting transformed digital data through the rock formation using amodulated waveform resembling a superposition of multiple waveforms.Communication is completed by receiving a waveform from the rockformation in response to said transmission, demodulating the receivedwaveform in to a plurality of demodulated values, and identifying packeterrors by using the plurality of demodulated values, the selectedtransform, and an error detection code value.

FIG. 9 illustrates a block diagram of a transmitter 910 and receiver912, according to various embodiments of the invention. FIG. 10illustrates a block diagram of a transmitter 1010 and receiver 1012,according to various embodiments of the invention. In this case, theorder of the components of the transmitter 610 and receiver 612 shown inFIG. 6 have been re-arranged. The location and composition of theconcatenated sequence 960 has also been changed. In addition, theestimate provided by the estimator 962 to the selector 644 comprisesboth estimated acquired data bits and estimated CRC bits. This permitsprocessing the acquired data (e.g., input bits 622) differently thanwhat is available with respect to the arrangements shown in FIGS. 6-8,providing essentially different transmitter/receiver combinations 910,912 and 1010, 1012. Thus, many embodiments may be realized.

An optimization metric may be calculated, where the controller uses atleast one PAPR of a transmitted modulated waveform to select at leastone transformation of digital data. The waveform may compriseinterpolated samples resulting from at least one interpolation filterconnected in series with an amplifier. Optimization may involve use of apredetermined criterion, such as a measure of PAPR for a transmittedmodulated waveform, or a characteristic of the filter, to guidetransform selection.

FIG. 11 illustrates a block diagram of a transmitter 1110 and receiver1112, according to various embodiments of the invention. FIG. 12illustrates a block diagram of a transmitter 1210 and receiver 1212,according to various embodiments of the invention. FIG. 13 illustrates ablock diagram of a transmitter 1310 and receiver 1312, according tovarious embodiments of the invention.

In this case, the order of the components of the transmitter 610 andreceiver 612 shown in FIG. 6 have been re-arranged. The composition ofthe concatenated sequence 1168 has also been changed, resulting in achange of the composition of the decoded data sequence 1170. Thispermits processing the acquired data (e.g., input bits 622) differentlythan what is available with respect to the arrangements shown in FIGS.6-8, providing essentially different transmitter/receiver combinations1110, 1112, 1210, 1212, and 1310, 1312. Thus, many embodiments may berealized.

In providing a service to its clients, an oil field services company maypractice various embodiments via a method of receiving digital datapackets through a rock formation that comprises sensing at least onephysical effect caused by the propagation of a superposition of aplurality of waveforms from a multiple waveform modulated electricalcurrent within the rock formation. The method may include demodulatingthe superposition of the plurality of waveforms into a plurality ofnumerical values, estimating digital values from said plurality ofdemodulated numerical values, transforming said estimated digital valuesusing at least one transform selected from a plurality of transforms.

The sensed physical effect may include sending an electrical voltagedrop across a distance in the rock formation, due to the current passingthrough the rock formation. Another physical effect that can be sensedincludes changes in magnetic fields observed using magnetometers.

In some embodiments, the estimated digital values may be scrambled usingat least one initial state value selected from a plurality of possibleinitial state values. Polynomial indicators can be selected from aplurality of possible polynomial indicators to configure the scrambler.Initial state values can be selected from a plurality of possibleinitial state values for this purpose, as well.

The process of selecting an initial state value/indicator, and/or apolynomial indicator may or may not take into account some of theestimated digital values. The receiver may or may not operate tocalculate CRC checksums using transformed, estimated digital values todetermine whether digital data packets have been correctly received. Thereceiver may or may not operate to search some or all possibletransforms, initial state SEED values/indicators, and/or polynomialindicators POLY to find a CRC value that indicates a correct decodingevent, or a checksum indicating a non-error condition.

FIG. 14 illustrates a block diagram of a transmitter 1410 and receiver1412, according to various embodiments of the invention. FIG. 15illustrates a block diagram of a transmitter 1510 and receiver 1512,according to various embodiments of the invention. FIG. 16 illustrates ablock diagram of a transmitter 1610 and receiver 1612, according tovarious embodiments of the invention.

In this case, the order of the components of the transmitter 610 andreceiver 612 shown in FIG. 6 have been re-arranged. The location andcomposition of the concatenated sequence 1474 has also been changed,resulting in a change of the composition of the decoded data sequence1478. This permits processing the acquired data (e.g., input bits 622)differently than what is available with respect to the arrangementsshown in FIGS. 6-8, providing essentially different transmitter/receivercombinations 1410, 1412, 1510, 1512, and 1610, 1612.

FIGS. 22-24 illustrate block diagrams of transmitters 2210, 2310, 2410and receivers 2212, 2312, 2412, according to various embodiments of theinvention. In this case, the order of the components of the transmitter1610 and receiver 1612 shown in FIG. 16 have been re-arranged. Thelocation and composition of the concatenated sequence 1474 has also beenchanged, resulting in a change of the composition of the decoded datasequence 1478 and 2478. This permits processing the acquired data (e.g.,input bits 622) differently than what is available with respect to thearrangements shown in FIGS. 14-16, providing essentially differenttransmitter/receiver combinations 2210, 2212, 2310, 2312, and 2410,2412.Thus, many embodiments may be realized.

In some embodiments, a method of formatting digital data packetsenabling transmission through a rock formation comprises receivingdigital data, calculating a CRC using said digital data, calculatingoptimization metrics for at least one transform and modulation schemeassociated with the transmission of electrical current through a rockformation. On or more transformations applied to the digital data may beselected form a plurality of transformations on the basis of theoptimization metric calculation results.

The current passing through the rock formation may be modulated byvarying a voltage using the transformed data. The optimization metricsmay be calculated using at least one initial scrambler state selectedfrom a plurality of possible initial scrambler states. The digital datamay be scrambled to produce scrambled data, and the current passingthrough the rock formation may be modulated by varying a voltage usingsaid scrambled data. In some embodiments, methods may comprisecalculating the optimization metrics using the CRC, and generatingparity data using a FEC encoder, further comprising calculating theoptimization metrics using said parity data.

In some embodiments, transformations are selected using a minimal orminimum optimization metric. In some embodiments, the optimizationmetric may be calculated using a maximal or maximum metric.

In some embodiments, the optimization metric may be calculated using thetransmission time of a formatted packet. In some embodiments, theoptimization metric may be calculated using the data rate of theformatted packet, further comprising interpolating said transformed datawith a filter, perhaps calculating optimization metrics use at least onecharacteristic of interpolating filtering. Still more embodiments may berealized.

FIG. 17 is a block diagram of apparatus 1700 according to variousembodiments of the invention. The apparatus 1700 may comprise any one ormore of the transmitters and/or receivers shown in FIGS. 6-16, and22-24. Moreover, any one or more of the transmitters and/or receiversshown in FIGS. 6-16, and 22-24 may include scramblers that comprise oneor more of the transforms shown in FIG. 1, operating on the bit streamformats shown in FIGS. 2-4, as appropriate.

Any of the transmitters described herein may comprise an interpolationfilter and/or an amplifier, to provide an amplified version of thetransmitter output signal voltage that results in propagating a currentin the geological formation. These components are not shown in many ofthe drawings so as not to obscure the composition of various embodimentsof the invention. Similarly, any of the receivers described herein maycomprise one or more preamplifiers and/or reception filters that provideamplified, filtered data to a demodulator. These components are also notshown in many of the drawings so as not to obscure the composition ofvarious embodiments of the invention.

In many embodiments, the apparatus 1700 comprises a combination ofdownhole instrumentation T, R, such as acoustic transmitters T₁-T₁′,T₂-T₂′ and T₃-T₃′ and acoustic receivers R1, R2, and R3, attached to adrill string 1704. The instrumentation T, R may also comprise otherkinds of instruments, such as magnetometers, electromagnetictransmitters/receivers, etc.

The apparatus 1700 may also include hardware logic 1740 and/or one ormore processors 1730, perhaps comprising a programmable drive and/orsampling control system. The logic 1740 can be used to acquire formationdata, such as resisitivity. The data can be stored in a memory 1750,perhaps using a database 1758.

A data transmitter and/or receiver 1744 (equivalent to or identical tothe transmitters and/or receivers of FIGS. 6-16, and 22-24) can be usedto communicate with a surface 1766 data processing system 1756, via asecond transmitter and/or receiver 1746 (which may also be equivalent toor identical to the transmitters and/or receivers shown in FIGS. 6-16,and 22-24). Thus, the apparatus 1700 may further comprise a datatransmitter 1744 (e.g., a telemetry transmitter or transceiver) totransmit boundary distance and resistivity formation parameters to asurface data processing system 1756. The communication may occur via anumber of channels 1760, such as the drill string, the drilling mud, thewell casing, and/or the geological formation surrounding the wellcasing. Some embodiments may include systems comprising multipleinstances of the apparatus 1700. For example, such systems may includeone or more transmitters and/or receivers 1744 below the surface 1766,and/or one or more transmitters and/or receivers 1746 above the surface1766.Thus, many embodiments may be realized.

For example, in the case of EMT, a MWD service provider may use anelectrical transmitting tool serially connected to the drill-string 1704to place a time-varying voltage potential across an insulator, such as aceramic spacer. The spacer may be located serially in the drill string1704 to electrically isolate the bit from the drill-string 1704 attachedto the surface rig, so as to produce time-varying electrical currents inthe surrounding rock formations. On the uplink connection (e.g., usingchannel 1760), the down-hole electrical tool varies the voltage acrossthis insulator and thus varies the current fields in the rock formation.A surface system receiver (e.g., receiver 1746) observes one or morevoltage drops or magnetic changes (e.g., using magnetometers) acrossdistances at the surface 1766, between the drill-string 1704 andspatially separated grounding spikes. The current used to communicateinformation may comprise any of the currents described herein.

If two-way communication is desired, a downlink connection (e.g., usingchannel 1760) transmits information from the surface rig to thedown-hole electrical tool. The surface system 1756 may use the potentialacross at least one distance at the surface 1766, perhaps using the sameset of grounding spikes and the drill string used for reception of theuplink information. Thus, the down-hole electrical tool is capable ofreceiving a signal by observing the potential across the insulatingspacer. Thus, additional embodiments may be realized.

For example, referring now to FIGS. 1-17, it can be seen that anapparatus 1700 may comprise a scrambler module to transform acquireddata into transformed data using at least one transform selected from aplurality of transforms according to an optimization metric calculationthat operates on single, fixed-length packets of the transformed dataand/or received data corresponding to the transformed data, and apreselected quality criterion threshold. The apparatus 1700 may comprisean amplifier to receive an electrical signal including the transformeddata, and to produce an amplified version of the electrical signal in ageological formation via a drill string.

In some embodiments, the apparatus 1700 may comprise an LFSRconfigurable to accomplish the at least one transform using at least oneof a selectable initial SEED value or a selectable polynomial indicatorPOLY. The apparatus 1700 may comprise a modulator to provide theelectrical signal by operating on the transformed data using OFDM orDSSS modulation. The apparatus 1700 may comprise a CRC processing moduleto generate a cyclic redundancy check value to be included in thetransformed data or the electrical signal.

In some embodiments, the apparatus 1700 may comprise an interpolationfilter to operate on the transformed data. The interpolation filter maybe located between the modulator and the amplifier, for example. Theapparatus 1700 may further comprise a portion of the drill string 1704to house the scrambler module and the amplifier. Thus, any of thecomponents of a down-hole tool 1762 may be housed by or attached to thedrill string 1704.

The apparatus 1700 may also comprise reception apparatus. For example,an apparatus 1700 may comprise a sensor (e.g., a preamplifier and/orfilter) to receive an amplified version of an electrical signal in ageological formation. The apparatus 1700 may further comprise adescrambler module to transform the electrical signal includingtransformed data into an estimated version of acquired data using atleast one transform defined by at least one of a seed value or apolynomial indicator. The at least one transform may be selected from aplurality of transforms according to an optimization metric calculationthat operates on single, fixed-length packets of the transformed dataand/or the estimated version, and a preselected quality criterionthreshold. The preselected quality criterion threshold may be based onat least one of a PAPR of the electrical signal, the transformed data,or an error rate of the estimated version.

The apparatus 1700 may further comprise a shift register (e.g., an LFSR)configurable to accomplish the at least one transform using at least oneof an initial seed value SEED or a polynomial indicator POLY containedin the electrical signal.

In some embodiments, the apparatus 1700 is electrically coupled to adrill string. The apparatus 1700 can be used to produce an electricalcurrent that propagates through a rock formation, and comprises a powersource, an amplifier electrically connected to the power source, theamplifier capable of pulsing an adjustable voltage output to producechanges in electrical current pulsing through the rock formation. Theapparatus 1700 further comprises a plurality of transforms that are usedto format digital data in packets. A controller (e.g., a hardwareprocessor) in the apparatus 1700 enables the amplifier to create aplurality of changes in electrical current passing through said rockformation, the current comprising multiple waveform modulation, whereinthe controller formats the digital data into packets using a transformselected from said plurality of transforms.

The multiple waveform modulation may comprise OFDM or DSSS modulation.The plurality of transforms may comprise one or more LFSRs configured toaccept at least one initial shift register value from a plurality ofpossible initial shift register values. The plurality of transforms maycomprise one or more configurable LSFRs to receive a polynomialindicator from a plurality of possible polynomial indicators describingfeedback connections.

The controller may operate to calculate one or more optimization metricsrelating to a predetermined criterion threshold for at least onetransform within the plurality of transforms. A memory in the apparatus1700 may be used to store one or more optimization metrics determined bythe predetermined criterion threshold.

The controller may operate to select a transform from said plurality oftransforms corresponding to a minimal or a minimum optimization metric.Similarly, the controller may operate to select a transform from saidplurality of transforms corresponding to a maximal or a maximumoptimization metric. The optimization metric may be the estimatedprobability of receiving the packet in error, or of receiving the packetcorrectly. The apparatus may further comprise a CRC processing moduleenabling said controller to include a CRC value within the packets offormatted digital data.

In some embodiments, the apparatus 1700 comprises a scrambler enabled toreceive at least one initial state indicator from a plurality ofpossible initial state indicators, to generate a sequence of numbers andtransform digital data using Galois Field arithmetic. The apparatus 1700may further comprise a controller enabling the amplifier to create aplurality of changes in electrical current passing through a rockformation resembling a multiple waveform modulation, wherein thecontroller optimizes using a predefined criterion that enables thescrambler to transform digital data into packets using an initial stateindicator selected from said plurality of possible initial stateindicators.

Calculating at least one optimization metric by the controller may useat least one PAPR of a transmitted modulated waveform corresponding toat least one transformation of the digital data. The predeterminedcriterion may thus include a measure of PAPR of a transmitted modulatedwaveform.

The apparatus 1700 may comprise at least one interpolation filter inseries with the amplifier. The controller may optimize using at leastone characteristic of the filter in the transform selection.

The apparatus 1700 may include a transform selector capable of selectingat least one transform from a plurality of transforms such that themodulated output voltage of the amplifier of at least one packet oftransformed digital values avoids non-linear distortion after processingby an interpolation filter, and the selected transform enables errordetection at the receiver.

The apparatus 1700 may comprise an initial state indicator selectorcapable of selecting at least one initial state indicator from aplurality of initial state indicators such that the modulated voltage ofat least one packet of transformed digital values avoids non-lineardistortion after processing by an interpolation filter, wherein saidselected transform enables error detection at the receiver.

In some embodiments, the apparatus 1700 electrically connected with adrill string may be configured to receive formatted digital datatransmitted via multiple waveform modulated electrical current through arock formation. The apparatus 1700 may comprise a sensor enabling thereception of a superposition of waveforms from said multiple waveformmodulated electrical current within said rock formation, a demodulatorenabling the estimation of said transmitted digital values from saidsuperposition of waveforms received by said sensor, a plurality oftransforms enabling at least one transformation of said receivedestimated digital values, and a controller (e.g., comprising processinghardware, such as a microprocessor or a digital signal processor) toselect at least one transform from said plurality of transforms andtransform received estimated digital values.

The plurality of transforms may comprise at least one LFSR configured toaccept at least one initial shift register value from a plurality ofpossible initial shift register values and/or to receive a polynomialindicator from a plurality of possible polynomial indicators describingfeedback connections.

The controller may operate to select at least one initial shift registervalue from a plurality of possible initial shift register values,enabling said transform selection. The controller may operate to selectat least one polynomial indicator from a plurality of possiblepolynomial indicators enabling said transform selection.

The controller may operate to select selects said selected initial shiftregister value and/or said selected polynomial indicator at least inpart based on said estimated transmitted digital values. The controllermay employ a plurality of LFSRs configured using a plurality ofpolynomial descriptors, respectively, corresponding to a plurality ofpolynomial indicators, also respectively.

The apparatus 1700 may comprise a CRC processing module enabling thechecking of at least one check value of said received estimated digitalvalues wherein said module also enables selection of transformedreceived estimated digital values from said plurality of transforms.

The apparatus 1700 may further comprise a scrambler to receive at leastone initial state indicator from a plurality of possible initial stateindicators, to generate a sequence of numbers and transform saidestimated digital values, and a controller to select at least oneinitial state indicator from said plurality of possible initial stateindicators used in the transformation of said estimated digital values.The scrambler may be configurable by receiving at least one polynomialindicator from a plurality of possible polynomial indicators describingthe configuration of the scrambler and at least one initial stateindicator from a plurality of possible initial state indicators, togenerate a sequence of numbers and transform said estimated digitalvalues in response to receiving a polynomial indicator and an initialstate indicator.

Some embodiments may comprise a system of multiple apparatus 1700—someof the apparatus 1700 operating as a transmitter, and some of theapparatus 1700 operating as a receiver. Such systems may operate as atransceiver and/or a repeater, as described previously.

Thus, a system to communicate through a rock formation may comprise atransmitter to modulate a current through a rock formation resemblingthe superposition of a plurality of waveforms. The system may furthercomprise a plurality of transforms accessible by said transmitterenabling the transformation of digital data. A receiver may be includedin the system, the receiver operating to demodulate, to select atransform from a plurality of transforms accessible by the receiver, andto transform said transformed digital data using an error detection codeto determine the digital data within at least one packet.

FIG. 18 illustrates a wireline system 1864 embodiment of the invention.FIG. 19 illustrates a drilling rig system 1964 embodiment of theinvention. Thus, the systems 1864, 1964 may comprise portions of a toolbody 1870 as part of a wireline logging operation, or of a downhole tool1924 as part of a downhole drilling operation. FIG. 18 shows a wellduring wireline logging operations. A drilling platform 1886 is equippedwith a derrick 1888 that supports a hoist 1890.

Drilling of oil and gas wells is commonly carried out using a string ofdrill pipes connected together so as to form a drilling string that islowered through a rotary table 1810 into a wellbore or borehole 1812.Here it is assumed that the drilling string has been temporarily removedfrom the borehole 1812 to allow a wireline logging tool body 1870, suchas a probe or sonde, to be lowered by wireline or logging cable 1874into the borehole 1812. Typically, the tool body 1870 is lowered to thebottom of the region of interest and subsequently pulled upward at asubstantially constant speed.

During the upward trip, at a series of depths the instruments (e.g., theinstruments T, R shown in FIG. 1700) included in the tool body 1870 maybe used to perform measurements on the subsurface geological formations1814 adjacent the borehole 1812 (and the tool body 1870). Themeasurement data can be communicated to a surface logging facility 1892for storage, processing, and analysis. Communication of the data mayoccur using any of the apparatus 1700 described herein. The loggingfacility 1892 may be provided with electronic equipment for varioustypes of signal processing, which may be implemented by any one or moreof the components of the apparatus 1700 in FIG. 1700. Similar formationevaluation data may be gathered and analyzed during drilling operations(e.g., during LWD operations, and by extension, sampling whiledrilling).

In some embodiments, the tool body 1870 comprises a formationresistivity tool for obtaining and analyzing resistivity measurementsfrom a subterranean formation through a wellbore. The formationresistivity tool is suspended in the wellbore by a wireline cable 1874that connects the tool to a surface control unit (e.g., comprising aworkstation 1854). The formation resistivity tool may be deployed in thewellbore on coiled tubing, jointed drill pipe, hard wired drill pipe, orany other suitable deployment technique.

Turning now to FIG. 19, it can be seen how a system 1964 may also form aportion of a drilling rig 1902 located at the surface 1904 of a well1906. The drilling rig 1902 may provide support for a drill string 1908.The drill string 1908 may operate to penetrate a rotary table 1810 fordrilling a borehole 1812 through subsurface formations 1814. The drillstring 1908 may include a Kelly 1916, drill pipe 1918, and a bottom holeassembly 1920, perhaps located at the lower portion of the drill pipe1918.

The bottom hole assembly 1920 may include drill collars 1922, a downholetool 1924, and a drill bit 1926. The drill bit 1926 may operate tocreate a borehole 1812 by penetrating the surface 1904 and subsurfaceformations 1814. The downhole tool 1924 may comprise any of a number ofdifferent types of tools including MWD (measurement while drilling)tools, LWD tools, and others.

During drilling operations, the drill string 1908 (perhaps including theKelly 1916, the drill pipe 1918, and the bottom hole assembly 1920) maybe rotated by the rotary table 1810. In addition to, or alternatively,the bottom hole assembly 1920 may also be rotated by a motor (e.g., amud motor) that is located downhole. The drill collars 1922 may be usedto add weight to the drill bit 1926. The drill collars 1922 may alsooperate to stiffen the bottom hole assembly 1920, allowing the bottomhole assembly 1920 to transfer the added weight to the drill bit 1926,and in turn, to assist the drill bit 1926 in penetrating the surface1904 and subsurface formations 1814.

During drilling operations, a mud pump 1932 may pump drilling fluid(sometimes known by those of skill in the art as “drilling mud”) from amud pit 1934 through a hose 1936 into the drill pipe 1918 and down tothe drill bit 1926. The drilling fluid can flow out from the drill bit1926 and be returned to the surface 1904 through an annular area 1940between the drill pipe 1918 and the sides of the borehole 1812. Thedrilling fluid may then be returned to the mud pit 1934, where suchfluid is filtered. In some embodiments, the drilling fluid can be usedto cool the drill bit 1926, as well as to provide lubrication for thedrill bit 1926 during drilling operations. Additionally, the drillingfluid may be used to remove subsurface formation 1814 cuttings createdby operating the drill bit 1926.

Thus, referring now to FIGS. 1-19, it may be seen that in someembodiments, the systems 1864, 1964 may include a drill collar 1922, adownhole tool 1924, and/or a wireline logging tool body 1870 to houseone or more apparatus 1700, similar to or identical to the apparatus1700 described above and illustrated in FIG. 17. Additional apparatus1700 may be included in a surface processing facility, such as theworkstation 1854. Thus, for the purposes of this document, the term“housing” may include any one or more of a drill collar 1922, a downholetool apparatus 1924, and a wireline logging tool body 1870 (all havingan outer wall, to enclose or attach to instrumentation, sensors, fluidsampling devices, pressure measurement devices, transmitters, receivers,and data acquisition systems). The apparatus 1700 may comprise adownhole tool, such as an LWD tool or MWD tool. The tool body 1870 maycomprise a wireline logging tool, including a probe or sonde, forexample, coupled to a logging cable 1874. Many embodiments may thus berealized.

For example, in some embodiments, a system 1864, 1964 may include adisplay 1896 to present resistivity information, both measured andpredicted, as well as database information, perhaps in graphic form. Asystem 1864, 1964 may also include computation logic, perhaps as part ofa surface logging facility 1892, or a computer workstation 1854, toreceive signals from transmitters and receivers, and otherinstrumentation to determine the distance to boundaries in the formation1814.

Thus, a system 1864, 1964 may comprise a downhole tool 1924, and one ormore apparatus 1700 attached to the downhole tool 1924, the apparatus1700 to be constructed and operated as described previously. Additionalapparatus 1700 may be included at the surface, perhaps in theworkstation 1854. In some embodiments, the downhole tool 1924 comprisesone of a wireline tool or an MWD tool.

The apparatus 1700, and any components included therein may all becharacterized as “modules” herein. Such modules may include hardwarecircuitry, and/or a processor and/or memory circuits, software programmodules and objects, and/or firmware, and combinations thereof, asdesired by the architect of the apparatus 1700 and systems 1864, 1964and as appropriate for particular implementations of variousembodiments. For example, in some embodiments, such modules may beincluded in an apparatus and/or system operation simulation package,such as a software electrical signal simulation package, a power usageand distribution simulation package, a power/heat dissipation simulationpackage, and/or a combination of software and hardware used to simulatethe operation of various potential embodiments.

It should also be understood that the apparatus and systems of variousembodiments can be used in applications other than for loggingoperations, and thus, various embodiments are not to be so limited. Theillustrations of apparatus 1700 and systems 1864, 1964 are intended toprovide a general understanding of the structure of various embodiments,and they are not intended to serve as a complete description of all theelements and features of apparatus and systems that might make use ofthe structures described herein.

Applications that may include the novel apparatus and systems of variousembodiments include electronic circuitry used in high-speed computers,communication and signal processing circuitry, modems, processormodules, embedded processors, data switches, and application-specificmodules. Such apparatus and systems may further be included assub-components within a variety of electronic systems, such astelevisions, cellular telephones, personal computers, workstations,radios, video players, vehicles, signal processing for geothermal toolsand smart transducer interface node telemetry systems, among others.Some embodiments include a number of methods.

For example, FIG. 20 is a flow chart illustrating several methods 2011according to various embodiments of the invention. In some embodiments,a computer-implemented method 2011 may begin at block 2021 withacquiring data, perhaps from a down-hole tool carrying a variety ofinstrumentation.

The method 2011 may continue on to block 2025 with formatting theacquired data into the single, fixed length packets, each of the packetsincluding at least one of an initial seed value or a polynomialindicator used in the transforming. The formatting can occur prior totransformation, or after transformation.

The method 2011 may continue on to block 2029 with calculating at leastone of a cyclic redundancy checksum or parity data using at least one ofthe acquired data or the transformed data. The activity at block 2029may further include inserting the at least one of the CRC or parity datainto at least one of the fixed-length packets.

The method 2011 may continue on to block 2033 with calculating anoptimization metric using at least one initial scrambler state selectedfrom a plurality of initial scrambler states corresponding to a fixedscrambler configuration and a selected modulation scheme.

The method 2011 may continue on to block 2037 to determine whether thecalculated optimization metric indicates and acceptable level of PAPR inthe data stream to be transmitted, or perhaps an acceptable level ofnon-linear distortion—in either case, when compared to a selectedquality criterion threshold.

Thus, if the threshold value is met at block 2037, the method 2011 maycontinue on to block 2041 with selecting at least one transform suchthat the amplified version has less than a selected amount of PAPR, ornon-linear distortion, or some other measure of signal qualitycorresponding to a preselected quality criterion threshold. If thethreshold value is not met at block 2037, then the method 2011 mayreturn to block 2033, to include selecting different values for initialscrambler states and/or transforms implemented by the scrambler.

The method 2011 may continue on to block 2045 from either of blocks 2037or 2041, to include transforming acquired data into transformed datausing at least one transform selected from a plurality of transformsaccording to an optimization metric calculation that operates on single,fixed-length packets of the transformed data, and a preselected qualitycriterion threshold.

The method 2011 may continue on to block 2047 with modulating theelectrical signal using the transformed data to provide the electricalsignal as a superposition of waveforms.

In some embodiments, the method 2011 includes filtering the transformeddata (e.g., using an interpolation filter), and then amplifying the dataprior to transmission, at block 2049.

The method 2011 may continue on to block 2053 with transmitting anamplified version of an electrical signal in a geological formation, theelectrical signal including the transformed data.

The method 2011 may continue on to block 2057 to include receiving anamplified version of an electrical signal in a geological formation, theelectrical signal including transformed data.

The method 2011 may continue on to block 2059, to include demodulatingthe amplified version as a superposition of a plurality of waveformsinto a plurality of numerical values comprising the transformed data.

The method 2011 may continue on to block 2061 to include configuring adescrambler to accomplish transformation (at block 2065) based on atleast one of an initial seed value or a polynomial indicator, eachselected according to a preselected quality criterion threshold, whichmay be the same or different as the threshold selected for thetransmission process.

The method 2011 may continue on to block 2065 to include transformingthe transformed data into an estimate of acquired data, the transformingusing at least one transform selected from a plurality of transformsaccording to an optimization metric calculation that operates on single,fixed-length packets of the transformed data and/or the estimate, andthe preselected quality criterion threshold.

The method 2011 may continue on to block 2069 to include parsing theestimate of acquired data to determine at least one of a cyclicredundancy checksum or parity data, and determining an error rate in theestimate based on the cyclic redundancy checksum and/or parity data.

At block 2073, the method 2011 may include comparing the error rate (orthe PAPR, or some other measure of quality) with the preselected qualitycriterion threshold. If the quality of the received data is found tomeet the desired, measurable level of quality, then the method 2011 mayend at block 2077. Otherwise, the method 2011 may include returning toblock 2061, to include re-configuring the descrambler by choosingdifferent initial SEED values, or different transform POLY values.

The activity at blocks 2061 and 2073 may thus comprise determining atleast one of an initial seed value or a polynomial indicator associatedwith the transformed data by attempting the transformation usingmultiple values of the initial seed value and/or the polynomialindicator until check data in the estimate indicates existence of acorrect value. Many additional embodiments may be realized.

For example, a method of formatting digital data packet enablingtransmission through a rock formation may comprise acquiring digitaldata, calculating a cyclic redundancy checksum using said digital data,calculating optimization metrics for at least one transform andmodulation scheme suitable to propagate electrical current passingthrough a rock formation, the current communicating a plurality oftransformations using said digital data, selecting a transformationusing said optimization metrics, and generating transformed data usingsaid digital data.

In another embodiment, a method of transmitting digital data packetsthrough a rock formation may comprise acquiring digital data,calculating a cyclic redundancy checksum using said digital data,calculating optimization metrics for at least one transform andmodulation scheme suitable for propagating electrical current through arock formation, the current communicating a plurality of transformationsusing said digital data, selecting a transformation using saidoptimization metrics, generating transformed data using said digitaldata, and modulating the current passing through the rock formation byvarying a voltage using said transformed data.

In another embodiment, a method of transmitting digital data packetsthrough a rock formation may comprise acquiring digital data,calculating a cyclic redundancy checksum using said digital data,calculating optimization metrics using at least one initial scramblerstate from a plurality of possible initial scrambler states of apredetermined scrambler configuration and a modulation scheme suitableto propagate electrical current through a rock formation, the currentcommunicating a plurality of transformations using said digital data.The method may further comprise selecting an initial scrambler state forsaid predetermined scrambler configuration using said optimizationmetrics, scrambling said digital data to produce scrambled data, andmodulating the current passing through the rock formation by varying avoltage using said scrambled data.

In another embodiment, a method of transmitting digital data packetsthrough a rock formation may comprise acquiring digital data,calculating a cyclic redundancy checksum using said digital data,calculating optimization metrics using at least one initial scramblerstate selected from a plurality of possible initial scrambler states forat least one scrambler configuration from a plurality of possiblescrambler configurations, and selecting a modulation scheme suitable topropagate electrical current through a rock formation, the currentcommunicating a plurality of transformations using said digital data.The method may further comprise selecting at least one scramblerconfiguration and at least one initial scrambler state using saidoptimization metrics, scrambling said digital data to produce scrambleddata, and modulating the current passing through the rock formation byvarying a voltage using said scrambled data.

Various methods may include calculating the optimization metrics using acyclic redundancy checksum and/or parity data. Thus, the methods maycomprise generating parity data using a forward error correctionencoder. The cyclic redundancy checksum may be calculated using saidparity data.

One or more transformations may be selected using a minimal or minimumoptimization metric. Similarly, one or more transformation may beselected using a maximal or maximum optimization metric.

The optimization metric may be calculated using the transmission time ofthe formatted packet and/or the data rate of the formatted packet. Someembodiments may comprise interpolating said transformed data with afilter, and perhaps calculating optimization metrics using at least onecharacteristic of said filtering.

In an embodiment, a method of receiving digital data packets through arock formation may comprise sensing at least one physical effect of thesuperposition of a plurality of waveforms from a multiple waveformmodulated electrical current within said rock formation, demodulatingsaid superposition of a plurality of waveforms into a plurality ofnumerical values, estimating digital values from said plurality ofdemodulated numerical values, transforming said estimated digital valuesusing at least one transform selected from a plurality of transforms.

In an embodiment, a method of receiving digital data packets through arock formation may comprise sensing at least one physical effect of thesuperposition of a plurality of waveforms from a multiple waveformmodulated electrical current within said rock formation, demodulatingsaid superposition of a plurality of waveforms into a plurality ofnumerical values, estimating digital values from said plurality ofdemodulated numerical values, scrambling said estimated digital valuesusing at least one initial state value selected from a plurality ofpossible initial state values, and selecting at least one initial statevalue from said plurality of possible initial state values.

In an embodiment, a method of receiving digital data packets through arock formation may comprise sensing at least one physical effect of thesuperposition of a plurality of waveforms from a multiple waveformmodulated electrical current within said rock formation, demodulatingsaid superposition of a plurality of waveforms into a plurality ofnumerical values, estimating digital values from said plurality ofdemodulated numerical values, selecting at least one polynomialindicator from a plurality of possible polynomial indicators,configuring a scrambler using at least in part the selected polynomialindicator, and scrambling said estimated digital values using at leastone initial state value selected from a plurality of possible initialstate values.

The selection of at least one initial state value may use at least aportion of said estimated digital values. Similarly, the selection of atleast one polynomial indicator may at least a portion of said estimateddigital values.

In some embodiments, the method may comprise calculating at least onecyclical redundancy checksum using transformed estimated digital valuesto enable determination of whether digital packets have been receivedcorrectly, or in error.

In some embodiments, the method may comprise determining a correctdecoding event for said received digital packet by calculating aplurality of cyclical redundancy checksums of a plurality of transformedestimated digital values, respectively, and ceasing additionalcalculations of cyclical redundancy checksums for a given receiveddigital packet upon the occurrence of a correct checksum check event.

In an embodiment, a method of communicating through a rock formation maycomprise selecting a transform from a plurality of transforms availableto a transmitter, transforming digital data using said selectedtransform enabling the receiver to perform an error-detection check,transmitting transformed digital data through a rock formation using amodulated waveform resembling a superposition of multiple waveforms,receiving the waveform from the rock formation, demodulating saidreceived waveform in to a plurality of demodulated values, andidentifying packet errors by using said plurality of demodulated values,said selected transform, and an error detection code value.

In an embodiment, a method of communicating through a rock formation maycomprise calculating at least one optimization metric relating to apredetermined optimization criterion, selecting a initial stateindicator from a plurality of initial state indicators available to thetransmitter using said at least one of optimization metric, scramblingdigital data using said selected initial state indicator enabling thereceiver to perform an error-detection check, transmitting saidscrambled digital data through a rock formation using a modulatedwaveform resembling a superposition of multiple waveforms, receiving awaveform from a rock formation in response to said transmitted modulatedwaveform, demodulating said received waveform into a plurality ofdemodulated values, and identifying packet errors by using saidplurality of demodulated values, said selected transform, and an errordetection code.

It should be noted that the methods described herein do not have to beexecuted in the order described, or in any particular order. Moreover,various activities described with respect to the methods identifiedherein can be executed in iterative, serial, or parallel fashion. Thevarious elements of each method can be substituted, one for another,within and between methods. Information, including parameters, commands,operands, and other data, can be sent and received in the form of one ormore carrier waves.

Upon reading and comprehending the content of this disclosure, one ofordinary skill in the art will understand the manner in which a softwareprogram can be launched from a computer-readable medium in acomputer-based system to execute the functions defined in the softwareprogram. One of ordinary skill in the art will further understand thevarious programming languages that may be employed to create one or moresoftware programs designed to implement and perform the methodsdisclosed herein. The programs may be structured in an object-orientatedformat using an object-oriented language such as Java or C#.Alternatively, the programs can be structured in a procedure-orientatedformat using a procedural language, such as assembly or C. The softwarecomponents may communicate using any of a number of mechanisms wellknown to those skilled in the art, such as application programinterfaces or interprocess communication techniques, including remoteprocedure calls. The teachings of various embodiments are not limited toany particular programming language or environment. Thus, otherembodiments may be realized.

For example, FIG. 21 is a block diagram of an article 2100 according tovarious embodiments of the invention, such as a computer, a memorysystem, a magnetic or optical disk, or some other storage device. Thearticle 2100 may include one or more processors 2116 coupled to amachine-accessible medium such as a memory 2136 (e.g., removable storagemedia, as well as any tangible, non-transitory memory including anelectrical, optical, or electromagnetic conductor) having associatedinformation 2138 (e.g., computer program instructions and/or data),which when executed by one or more of the processors 2116, results in amachine (e.g., the article 2100) performing any actions described withrespect to the apparatus, systems, and methods of FIGS. 1-20.

In some embodiments, the article 2100 may comprise one or moreprocessors 2116 coupled to a display 2118 to display data processed bythe processor 2116 and/or a wired or wireless transceiver 1700 (e.g., adownhole telemetry transceiver) to receive and transmit data processedby the processor.

The memory system(s) included in the article 2100 may include memory2136 comprising volatile memory (e.g., dynamic random access memory)and/or non-volatile memory. The memory 2136 may be used to store data2140 processed by the processor 2116, such as data acquired by down-holetool instrumentation.

In various embodiments, the article 2100 may comprise communicationapparatus 2122, which may in turn include amplifiers 2126 (e.g.,preamplifiers or power amplifiers) and/or filters (e.g., interpolationfilters, noise reduction filters, etc.). Signals 2142 received ortransmitted by the communication apparatus 2122 may be processedaccording to the methods described herein.

Many variations of the article 2100 are possible. For example, invarious embodiments, the article 2100 may comprise a downhole tool, suchas the tool apparatus 1700 shown in FIG. 17.

Using the apparatus, systems, and methods disclosed herein may providereduced transmitter hardware complexity (and expense) by reducing thePAPR of communication signals, and thus the dynamic range of thetransmitter. The number of usable sub-channels and/or spreading codesmay be increased, by minimizing the impact of each additionalchannel/code on the overall PAPR of the communication system. In a powerconstrained system, system throughput may be improved by reducing thepower back-off needed to maintain the time-domain aggregate signalwithin the transmitter's dynamic range and/or facilitate the avoidanceof non-linear distortion, e.g. clipping of peak voltages. Increasedcustomer satisfaction may result.

The accompanying drawings that form a part hereof, show by way ofillustration, and not of limitation, specific embodiments in which thesubject matter may be practiced. The embodiments illustrated aredescribed in sufficient detail to enable those skilled in the art topractice the teachings disclosed herein. Other embodiments may beutilized and derived therefrom, such that structural and logicalsubstitutions and changes may be made without departing from the scopeof this disclosure. This Detailed Description, therefore, is not to betaken in a limiting sense, and the scope of various embodiments isdefined only by the appended claims, along with the full range ofequivalents to which such claims are entitled.

Such embodiments of the inventive subject matter may be referred toherein, individually and/or collectively, by the term “invention” merelyfor convenience and without intending to voluntarily limit the scope ofthis application to any single invention or inventive concept if morethan one is in fact disclosed. Thus, although specific embodiments havebeen illustrated and described herein, it should be appreciated that anyarrangement calculated to achieve the same purpose may be substitutedfor the specific embodiments shown. This disclosure is intended to coverany and all adaptations or variations of various embodiments.Combinations of the above embodiments, and other embodiments notspecifically described herein, will be apparent to those of skill in theart upon reviewing the above description.

The Abstract of the Disclosure is provided to comply with 37 C.F.R.§1.72(b), requiring an abstract that will allow the reader to quicklyascertain the nature of the technical disclosure. It is submitted withthe understanding that it will not be used to interpret or limit thescope or meaning of the claims. In addition, in the foregoing DetailedDescription, it can be seen that various features are grouped togetherin a single embodiment for the purpose of streamlining the disclosure.This method of disclosure is not to be interpreted as reflecting anintention that the claimed embodiments require more features than areexpressly recited in each claim. Rather, as the following claimsreflect, inventive subject matter lies in less than all features of asingle disclosed embodiment. Thus the following claims are herebyincorporated into the Detailed Description, with each claim standing onits own as a separate embodiment.

1. An apparatus, comprising: a scrambler module to transform acquireddata into transformed data using at least one transform selected from aplurality of transforms according to an optimization metric calculationthat operates on single, fixed-length packets of the transformed dataand/or received data corresponding to the transformed data, and apreselected quality criterion threshold; and an amplifier to receive anelectrical signal including the transformed data, and to produce anamplified version of the electrical signal in a geological formation viaa drill string.
 2. The apparatus of claim 1, further comprising: alinear feedback shift register configurable to accomplish the at leastone transform using at least one of a selectable initial seed value or aselectable polynomial indicator.
 3. The apparatus of claim 1, furthercomprising: a modulator to provide the electrical signal by operating onthe transformed data using orthogonal frequency division multiplexmodulation or direct sequence spread spectrum modulation.
 4. Theapparatus of claim 1, further comprising: a cyclic redundancy checkprocessing module to generate a cyclic redundancy check value to beincluded in the transformed data or the electrical signal.
 5. Theapparatus of claim 1, further comprising: an interpolation filter tooperate on the transformed data.
 6. The apparatus of claim 1, furthercomprising: a portion of the drill string to house the scrambler moduleand the amplifier.
 7. An apparatus, comprising: a sensor to receive anamplified version of an electrical signal in a geological formation; anda descrambler module to transform the electrical signal includingtransformed data into an estimated version of acquired data using atleast one transform defined by at least one of a seed value or apolynomial indicator, the at least one transform selected from aplurality of transforms according to an optimization metric calculationthat operates on single, fixed-length packets of the transformed dataand/or the estimated version, and a preselected quality criterionthreshold.
 8. The apparatus of claim 7, wherein the preselected qualitycriterion threshold is based on at least one of apeak-to-average-power-ratio of the electrical signal, the transformeddata, or an error rate of the estimated version.
 9. The apparatus ofclaim 7, further comprising: a shift register configurable to accomplishthe at least one transform using at least one of an initial seed valueor a polynomial indicator contained in the electrical signal.
 10. Acomputer-implemented method, comprising: transforming acquired data intotransformed data using at least one transform selected from a pluralityof transforms according to an optimization metric calculation thatoperates on single, fixed-length packets of the transformed data, and apreselected quality criterion threshold; and transmitting an amplifiedversion of an electrical signal in a geological formation, theelectrical signal including the transformed data.
 11. The method ofclaim 10, further comprising: formatting the acquired data into thesingle, fixed length packets, each of the packets including at least oneof an initial seed value or a polynomial indicator used in thetransforming.
 12. The method of claim 10, further comprising:calculating at least one of a cyclic redundancy checksum (CRC) or paritydata using at least one of the acquired data or the transformed data;and inserting the at least one of the CRC or parity data into at leastone of the fixed-length packets.
 13. The method of claim 10, furthercomprising: calculating the optimization metric using at least oneinitial scrambler state selected from a plurality of initial scramblerstates corresponding to a fixed scrambler configuration and a selectedmodulation scheme.
 14. The method of claim 10, further comprising:modulating the electrical signal using the transformed data to providethe electrical signal as a superposition of waveforms.
 15. The method ofclaim 10, further comprising: selecting the at least one transform suchthat the amplified version has less than a selected amount of non-lineardistortion corresponding to the preselected quality criterion threshold.16. A computer-implemented method, comprising: receiving an amplifiedversion of an electrical signal in a geological formation, theelectrical signal including transformed data; and transforming thetransformed data into an estimate of acquired data, the transformingusing at least one transform selected from a plurality of transformsaccording to an optimization metric calculation that operates on single,fixed-length packets of the transformed data and/or the estimate, and apreselected quality criterion threshold.
 17. The method of claim 16,further comprising: configuring a descrambler to accomplish thetransforming based on at least one of an initial seed value or apolynomial indicator, each selected according to the preselected qualitycriterion threshold.
 18. The method of claim 16, further comprising:parsing the estimate of acquired data to determine at least one of acyclic redundancy checksum (CRC) or parity data; determining an errorrate in the estimate based on the CRC and/or parity data; and comparingthe error rate with the preselected quality criterion threshold.
 19. Themethod of claim 16, further comprising: determining at least one of aninitial seed value or a polynomial indicator associated with thetransformed data by attempting the transforming using multiple values ofthe initial seed value and/or the polynomial indicator until check datain the estimate indicates existence of a correct value.
 20. The methodof claim 16, further comprising: demodulating the amplified version as asuperposition of a plurality of waveforms into a plurality of numericalvalues comprising the transformed data.